NASA: Huge Mars Rover's Sky Crane Landing Was 'Least Crazy' Idea

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The stunningly intricate series of maneuvers that will drop
NASA's Curiosity rover onto the Martian surface Sunday (Aug. 5)
looks pretty reasonable when you consider the alternatives,
experts say.

Late Sunday night, the 1-ton Curiosity rover's spacecraft will
barrel into the Red Planet's atmosphere going about 13,000 mph
(21,000 kph). A huge parachute will deploy about 7 miles (11
kilometers) above the ground, slowing the vehicle down to 200 mph
(320 km) or so. Rocket engines will then fire, reducing the
craft's descent speed to less than 2 mph (3.2 kph).

Finally, the $2.5 billion rover will be lowered to the surface on
cables. When Curiosity's six wheels hit the red dirt inside Mars'
huge Gale Crater, its " sky
crane " descent stage will fly off and crash-land
intentionally a safe distance away. NASA has dubbed the maneuver
" seven
minutes of terror."

Curiosity is the largest rover ever sent to explore another
world, and this sequence was designed specifically to accommodate
its huge bulk. The landing method may seem incredibly
complicated, but the mission team is confident it will work — and
it was the best available option, engineers said. [ Photos:
How Curiosity's Crazy Landing Works ]

"It looks a little bit crazy. I promise you, it is the least
crazy of the methods you could use to land a rover the size of
Curiosity on
Mars," Adam Steltzner, of NASA's Jet Propulsion Laboratory in
Pasadena, Calif., told reporters today (Aug. 2). Steltzner is
entry, descent and landing phase lead for Curiosity's mission,
which is known as the Mars Science Laboratory (MSL).

To illustrate the point, Steltzner discussed the two chief
alternatives to the
sky crane Mars landing system. The first of these, he said,
was putting Curiosity down on legs, as NASA did on Mars with its
two Viking landers in the 1970s and the Phoenix lander in 2008.

But the team determined that Curiosity — which aims to determine
if the Gale Crater area can, or ever could, support microbial
life — is just too big to land safely on legs.

"When you stick a rover the size of Curiosity on the deck of a
legged lander, it becomes very unstable, and you need to land on
a flat-top spot to be able to make that happen," Steltzner said.

The other leading alternative was to send Curiosity bouncing
across the Martian landscape cushioned inside airbags. The twin
Spirit and Opportunity Mars rovers landed this way in January
2004.

Again, however, Curiosity's heft nixed this idea. It weighs about
five times as much as either Spirit or Opportunity.

"Unfortunately, we don't have fabric here on Earth strong enough
to build airbags that would work for a rover the size of
Curiosity," Steltzner said. "The bags would shred, not giving
Curiosity any protection."

So MSL's entry, descent and landing team was left with the sky
crane method, which has performed well in all of the engineers'
simulations.

"We've become quite fond of it, and we're fairly confident that
Sunday night will be a good night for us," Steltzner said.

Curiosity is due to land on Mars at 10:31 p.m. PDT on Sunday,
Aug. 5 (1:31 a.m. EDT, 0531 GMT on Aug. 6).